Allow to opt-out from X11 session wrapping

While `startx` is a reasonable default, it might be missing from the
system or in confict with an already deployed solution for launching
X11 sessions.
`--no-xsession-wrapper` disables any modifications of the X11 session
commands.

README.md

@@ -17,6 +17,8 @@ Options:
         --xsession-wrapper 'CMD [ARGS]...'
                         wrapper command to initialize X server and launch X11
                         sessions (default: startx /usr/bin/env)
+        --no-xsession-wrapper
+                        do not wrap commands for X11 sessions
     -w, --width WIDTH   width of the main prompt (default: 80)
     -i, --issue         show the host's issue file
     -g, --greeting GREETING

contrib/man/tuigreet-1.scd

@@ -33,6 +33,9 @@ tuigreet - A graphical console greeter for greetd
 	By default, *startx /usr/bin/env* will be prepended to all X11 session
 	commands.
 
+*--no-xsession-wrapper*
+	Do not wrap commands for X11 sessions.
+
 *-w, --width COLS*
 	Number of columns the main prompt area should take on the screen.
 

src/greeter.rs

@@ -297,6 +297,7 @@ impl Greeter {
     opts.optopt("s", "sessions", "colon-separated list of Wayland session paths", "DIRS");
     opts.optopt("x", "xsessions", "colon-separated list of X11 session paths", "DIRS");
     opts.optopt("", "xsession-wrapper", xsession_wrapper_desc.as_str(), "'CMD [ARGS]...'");
+    opts.optflag("", "no-xsession-wrapper", "do not wrap commands for X11 sessions");
     opts.optopt("w", "width", "width of the main prompt (default: 80)", "WIDTH");
     opts.optflag("i", "issue", "show the host's issue file");
     opts.optopt("g", "greeting", "show custom text above login prompt", "GREETING");
@@ -409,7 +410,9 @@ impl Greeter {
       self.session_paths.extend(env::split_paths(&dirs).map(|dir| (dir, SessionType::X11)));
     }
 
-    self.xsession_wrapper = self.option("xsession-wrapper").or_else(|| Some(DEFAULT_XSESSION_WRAPPER.to_string()));
+    if !self.config().opt_present("no-xsession-wrapper") {
+      self.xsession_wrapper = self.option("xsession-wrapper").or_else(|| Some(DEFAULT_XSESSION_WRAPPER.to_string()));
+    }
 
     if self.config().opt_present("issue") {
       self.greeting = get_issue();